Previously, many types of torque wrenches have been used to provide an effective means for tightening threaded fasteners to a predetermined value of tension. In the past mechanical wrenches have utilized spring tension to determine the amount of torque applied to tighten a threaded fastener. These wrenches historically employ a mechanism that uses some type of metallic member that is released when the desired torque is obtained, thus striking the housing or other part of the wrench to produce a distinct mechanical release and to produce a distinct sound, such as an audible "click". Further, industry has developed specialty wrenches that include electronic means for measuring the amount of torque applied to a structure in response to the manual application of force independent of the position of the user's hand.
A search of the prior art did not disclose any patents that read directly on the claims of the instant invention, however the following U.S. patents are considered related:
U.S. Pat. No. INVENTOR ISSUED 5,741,186 Tatsuno 21 April 1998 5,662,012 Garbviac 2 September 1997 5,643,089 Hummel 1 July 1997 5,156,072 Muralidharan 20 October 1992 5,142,951 Walton 1 September 1992 4,982,612 Rittmann 8 January 1991 4,864,841` Heyraud 12 September 1989 Foreign patent Documents 3534520 Germany 9 April 1987 2829009 Germany 10 January 1980 2651636 Germany 24 May 1978 2338304 Germany 30 October 1975 0372247 European Patent 9 November 1989 0360894 European Patent 9 September 1988
Tatsuno in U.S. Pat. No. 5,741,186 teaches an impulse torque generator for a hydraulic impulse torque wrench. The generator includes a liner driven by a rotor. The liner has an inner cavity having two pairs of sealing surfaces around its inner peripheral surface. A main shaft extends through the liner having projections and driving blades that generate the torque on the shaft by abutting the projections.
Grabivac discloses in U.S. Pat. No. 5,662,012 an adjustable click-type torque wrench. Adjustment is accomplished by a carrier nut engaging the rear end of a lever arm that is contiguous with a spring.
U.S. Pat. No. 5,643,089, issued to Hummel, discloses a non-jarring design that resets the wrench without jarring the output shaft after it delivers the preset maximum torque. The wrench utilizes interchangeable output shafts such that a variety of different drive tips may be employed with the same handle. The cam surfaces of the output shafts have unique surfaces to accommodate varying torque value.
Muralidharan in U.S. Pat. No. 5,156,072 discloses a mechanical torque wrench that employs a plurality of levers. A first lever is journalled to an output shaft for rotation and the remaining levers are pivotally secured to a housing adjacent with their ends along the longitudinal direction of the wrench handle. The torque value is adjusted by changing the force to be overcome by the lever to the pivot.
U.S. Pat. No. 5,142,951 issued to Walton discloses a torque wrench that utilizes a hydraulic piston-cylinder assembly, which rotates a member around an axis located perpendicular to the wrench body. A reaction member is attached to the body and is pivoted relative to the axis between different positions extending angularity out from the body.
Rittmann in U.S. Pat. No. 4,982,612 teaches a torque measuring wrench using a deflection beam, with four strain gauges mounted thereon. One gauge is positioned on a reduced cross-sectional area and the other is closer to the ratchet head. A tubular handle encloses a battery-powered control circuit having indicating means, which provides measurements that are independent of the position along the handle at which the force is applied.
U.S. Pat. No. 4,864,841 issued to Heyraud discloses an electronic wrench that employs two strain gauges that are placed on either side of a crosswise plane. An electronic circuit determines and stores a constant factor for calibration, and the value of torque is measured by the strain gauges and displayed.
For background purposes and as indicative of the art to which the invention is related reference may be made to the remaining cited foreign patents.